EP-A-0 567 957 A describes a computer with a power control unit that when connected to a power source can be placed in a run mode in which the computer is fully powered up, and a standby mode in which only part of the computer is powered, this part not including the microprocessor. The power control unit transitions from its run mode to its standby mode either automatically if no keyboard key is pressed for a predetermined time interval, or as a result of a user pressing a predetermined key of the keyboard. When the power control unit is in its standby mode, the pressing of any keyboard key transitions the power control unit to its run mode--however, if that key is detected as being continuously pressed, this is taken as indicating an unintentional key operation and the power control unit is returned to its standby mode.
It will be appreciated that in the foregoing arrangement, the keyboard controller must be kept powered in the standby mode in order to detect the pressing of any key.
It may also be noted that the problem of unintentional powering on of the computer is increased by having operation of any key cause such powering on. If operation of only one key resulted in powering on of the computer, then the risk of unintentional powering up of the computer would be reduced; however, this would also require interpretation of the key code output by the keyboard controller as this, in turn calls for energy-consuming circuitry.
It is an object of the present invention to overcome at least some of the above-described disadvantages of the prior art.
The present invention is described hereinafter in the context of (but not limited to) a computer with a power provisioning system including a small standby power supply as well as the main power supply. Such an arrangement is known in the art, the standby supply being intended to be energised from an external power source like the main supply of the computer but with the difference that the standby supply is always energised when the power lead is plugged into the external supply, regardless of the on/off state of what is presented to the user as the on/off switch of the computer. This standby supply powers the real time clock of the computer for as long as the power lead is plugged into the external power source, thereby reducing power drain on the internal battery normally provided for driving this clock when the main supply is powered down. In fact, it is also known to use this standby supply to power an electronic switch that controls the supply of power from the external power source to the main supply, this arrangement thereby avoiding the need to have the on/off switch operated by the user directly switch the external power source.